Cardiac monitoring and therapy using a device for providing pressure treatment of sleep disordered breathing

ABSTRACT

A method of using CPAP equipment to sense cardiogenic oscillations in a patient&#39;s airflow, and to monitor and treat the patient&#39;s cardiac condition. The apparatus diagnoses cardiac morbidity conditions, such as the existence of arrhythmias or other cardiac abnormalities, and influences and optimizes cardiac stroke volume. The apparatus further monitors pulse-transit time, changes in the heart pre-ejection period, and the duration of the cardiac cycle.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 10/598,255, filed on Apr. 20, 2007, which application is anational phase entry under 35 U.S.C. §371 of International ApplicationNo. PCT/AU05/00248 filed Feb. 24, 2005, published in English, whichclaims priority from U.S. Provisional Patent Application No. 60/547,812filed Feb. 25, 2004, all of which are hereby incorporated herein byreference.

BACKGROUND OF THE INVENTION

Cessation of breathing during sleep for more than 10 seconds is calledan “apnea,” which leads to decreased blood oxygenation and disruption ofsleep. Apneas are traditionally categorized as central, where there isno respiratory effort, or obstructive sleep apnea (OSA), where there isrespiratory effort but the airway is blocked. With purely centralapneas, the airway is patent (or open), but the patient is notattempting to breathe. With other central apneas and all obstructiveapneas, the airway is not patent (i.e., it is occluded). The occlusionis usually at the level of the tongue or soft palate.

The common form of treatment of apneas is the administering ofcontinuous or variable positive airway pressure (referred to hereingenerally as CPAP). Devices that provide CPAP treatment are described inU.S. Pat. Nos. 5,704,345, 6,532,957, 6,575,163, 6,484,719, 6,688,307,and 6,532,959, incorporated herein by reference. The procedure foradministering CPAP treatment has been well documented in both thetechnical and patent literature. Briefly stated, CPAP treatment acts asa pneumatic splint of the airway by the provision of positive pressure,usually in the range 4-20 cm H₂O. The air is supplied to the airway by amotor driven blower whose outlet passes air via a delivery tube or hoseto a nose (and/or mouth) mask sealingly engaged to a patient's face. Anexhaust port is provided in the delivery tube proximate to the mask.

More sophisticated forms of CPAP, such as bi-level CPAP andself-titrating CPAP, are described in U.S. Pat. Nos. 5,148,802 and5,245,995, respectively.

CPAP therapy is also known to be beneficial to some cardiac pathology,for example, congestive heart failure. By boosting intrathoracicpressure, CPAP offers various (potential) direct benefits in heartfailure, for example, impeding venous return (reducing preload),reducing the systolic pressure gradient against which the left ventriclemust pump (reduced afterload), and reducing left-ventricular trans-muralpressure (improved contractile efficiency). In addition, CPAP may offerindirect benefits to heart-failure patients, e.g., to counter pulmonaryedema, to increase lung volume (may aid ventilatory stability inCheyne-Stokes respiration), and in patients with a disposition toobstructive apnea, to reduce sympathetic activation through preventionof repetitive OSA.

Various techniques are known for detecting abnormal breathing patternsindicative of obstructed breathing. U.S. Pat. No. 5,245,995, forexample, describes how snoring and abnormal breathing patterns can bedetected by inspiration and expiration pressure measurements whilesleeping, thereby leading to early indication of pre-obstructiveepisodes or other forms of breathing disorder. Patterns of respiratoryparameters are monitored, and CPAP pressure is raised on the detectionof pre-defined patterns to provide increased airway pressure to subvertthe occurrence of the obstructive episodes and the other forms ofbreathing disorder.

Central apneas need not involve an obstruction of the airway, and oftenoccur during very light sleep and in patients with various cardiac,cerebrovascular and endocrine conditions unrelated to the state of theupper airway. In cases where the apnea is occurring without obstructionof the airway, there may be little benefit in increasing CPAP pressure,in contrast to an obstructive apnea.

To differentiate between central and obstructed apneas, U.S. Pat. No.6,029,665, incorporated herein by reference, teaches a CPAP system thatmonitors pulsatile airflow during the apnea event. With each beat of theheart, of the order of 66 ml of blood is ejected from the chest overabout 0.3 sec, producing a pulsatile blood flow out of the chest of theorder of 0.22 l/sec peak flow. If the chest wall were rigid this wouldcreate a partial vacuum in the chest cavity, and, if the upper airwaywere open and had zero flow resistance, a similar quantity of air wouldbe sucked in through the trachea. In practice, the chest wall is nottotally rigid, and the airways have finite airflow resistance.Consequently the measurable airflow (or cardiogenic oscillation) witheach beat of the heart is of the order of 0.02 to 0.1 I/sec.

If there is a central apnea with an open airway, the device of the '665patent will sense cardiogenic oscillations in the air pressure, anddetermine that an unobstructed central apnea event has occurred.Conversely, if the airway is closed, the pressure waveform will not haveany noticeable cardiogenic oscillations, and the device of the '665patent will determine that the apnea event was an obstructed event.

Implementing the apparatus and method of the '665 patent prevents theinappropriate increase in the splinting CPAP air pressure during acentral apnea, thereby preventing an unnecessary increase in pressurethat may otherwise reflexively inhibit breathing and further aggravatethe breathing disorder. The device is also used in a diagnostic mode,using nasal cannulae in the place of a face mask, where measurements ofapneas, patency, and partial obstruction are logged, but no CPAPtreatment is effected. The data provides a physician with the ability todiagnose conditions such as OSA and upper airway resistance syndrome.

Neither the '665 patent nor other prior art utilizes measurements ofcardiogenic oscillations in a CPAP patient's airflow for monitoring ortreating conditions related to cardiac health.

BRIEF SUMMARY OF THE INVENTION

It is an object of the invention to utilize a CPAP device that treatssleep disordered breathing (SDB) also as a cardiac treatment device bymonitoring cardiac signals in a patient's airflow to determine cardiachealth.

More specifically, it is an object of the invention to monitor thecardiac signals to screen and diagnose cardiac morbidity conditions,such as the existence of arrhythmias, and to influence and optimizecardiac stroke volume.

It is a further object to monitor pulse-transit time, changes in theheart pre-ejection period, and the duration of the cardiac cycle.

To satisfy the recited objectives, a method is disclosed of sensingcardiogenic oscillations in a patient's airflow and monitoring thepatient's cardiac condition from the cardiogenic oscillations. Theapparatus diagnoses cardiac morbidity conditions, such as the existenceof arrhythmias or other cardiac abnormalities and influences andoptimizes cardiac stroke volume. The apparatus further monitorspulse-transit time, changes in the heart pre-ejection period, and theduration of the cardiac cycle.

BRIEF DESCRIPTION OF THE DRAWINGS

To further satisfy the recited objectives, a detailed description oftypical embodiments of the invention is provided with reference toappended drawings that are not intended to limit the scope of theinvention, in which:

FIG. 1 is a diagram of an apparatus that treats sleep disorderedbreathing during sleep and monitors cardiac signals in a CPAP patient'sairflow to assess cardiac health and treat cardiac conditions; and

FIG. 2 is a graph illustrating, over a selected time period, airflow,ECG and mask air pressure.

DETAILED DESCRIPTION

Turning to FIG. 1, a device for treating SDB during sleep is disclosedthat is capable of carrying out the features of the invention (such as aCPAP device), including sensing cardiogenic oscillations in airpressure/flow readings to determine whether an apnea event is central orobstructed. Mask flow is measured using a flow sensor 4 f and/orpressure sensor 4 p with a pneumotachograph and differential pressuretransducer or similar device. A flow signal F(t) is derived and maskpressure is measured at a pressure tap using a pressure transducer toderive a pressure signal P_(mask)(t). The pressure sensor 4 p and flowsensor 4 f have been shown only symbolically in FIG. 1 since thoseskilled in the art would understand how to measure flow and pressure.

Flow F(t) and pressure P_(mask) signals are sent to a controller ormicroprocessor 6 which then determines how to adjust the blower. Thecontroller 6 may include integrated circuits, a memory and/or otherinstruction or data storage medium. Programmed instructions with controlmethodology may be coded on integrated chips in the memory of the device(e.g., firmware) or loaded as software.

The pressure delivery device includes a blower 8, which preferably is animpellor. The impellor 8 is controlled by a servo 10, receives ambientair through an inlet 12 and delivers pressurized air through an outlet14 defined by an air delivery conduit 16 and a mask 18 with anintegrated exhaust vent 20. The impellor, motor, and controller assemblydefine a blower assembly and are located within the blower housing 22.Various switches 24 and displays 26 are provided in the blower housing.A number of sensors are provided within the blower to monitor, amongother things, snore 28, motor speed 30, and motor current 32. Variousdevices known in the art can serve as these types of sensors. Acommunication interface 34 allows data to be transferred between theapparatus and an external device, such as a computer or controller.

If cardiogenic oscillations are not reflected in the pressure in apatient's mask during an apnea event, then the patient may beexperiencing an obstructed central apnea event or an obstructed apneaevent with respiratory effort. The above measuring technique, by itself,is incapable of differentiating the two conditions so that an indicatorof respiratory effort is required. One type of known detector detectswhen the skin in the suprastemal notch is sucked inwards (duringinhalation) and when the skin bulges outward (during expiratoryefforts). Such a device is taught in U.S. Pat. No. 6,445,942,incorporated herein by reference, which can be used to identify theoccurrence of a central apnea.

FIG. 2 illustrates traces that may be recorded by appropriate equipment.Trace 42 illustrates a patient's electrocardiogram (ECG), trace 44 isthe CPAP patient's airflow and trace 46 is the patient's air pressure asmeasured using the CPAP treatment device. (Either or both of airflow andpressure may be monitored.) In the vicinity of numeral 47, therespiratory flow hovers around zero, indicating an apnea event. The airpressure trace 46 still exhibits cardiogenic oscillations 48 indicativeof an open airway (unobstructed) central apnea event.

When monitoring air pressure 46, a band filter may be used. A suitablefilter rejects signals of 30 Hz or lower (i.e., rejects those signalswhich are generally associated with respiration and physical movement ofthe patient) and also rejects signals higher than 60 Hz (i.e., rejectthose signals which are generally associated with system noise ratherthan being representative of cardiogenic events).

Once cardiogenic information is in hand, it can be used to better manageconventional triggering circuits for a bi-level CPAP ventilator (whichtypically adjust the ventilator in response to inspiratory andexpiratory flow), since distortions of air flow measurementsattributable to cardiogenic oscillations can be ignored. Of particularinterest is the identification and filtering out of cardiogenic flowoscillation occurring at the end-expiration (i.e., cardiogenicoscillation signals occurring at a part of the respiratory phase when itis desirable for the ventilator to most accurately cycle from expirationto inspiration in accordance with the applicable treatment algorithm).

Studying the presence of cardiogenic oscillations and, if present, theiramplitude and frequency, during an open apnea event over a period ofseveral seconds, without the complication of the concurrent existence ofthe airflow signal, provides information concerning the patient'scardiac condition. A medical practitioner can assess the patient'scardiac condition and treatment needs given the known association ofcentral apneas and cardiac morbidity.

While the cardiogenic airflow may be detected during any portion of thepatient's respiratory cycle, the best resolution of the cardiogenicoscillations 48 occurs during the middle to end of the expirationportion 49 of the patient's breath. Monitoring the signal in only thisrelatively small window simplifies the processing needed to achieve therequisite signal resolution. Indeed, for some applications, it may besufficient to monitor cardiogenic oscillations during only that portionof the respiratory cycle, i.e., significantly less than all theheartbeats per breath.

To locate the middle to end of the expiratory cycle, the controllerdetects the start of a new expiration cycle (with a threshold detectorthat detects the zero line transition), and identifies the end of theexhalation based on the recent averaged lapsed time of breathing cycles.Alternatively, the later portion of exhalation may be isolated usingcontinuous phase monitoring of the patient's breathing, as disclosed inthe '957 patent referenced above.

Through long term monitoring of the cardiogenic oscillations 48,irregularities in the force or rhythm of the heartbeat signal can bedetected, which enables the determination of an arrhythmia. Theamplitude and/or frequency of the signal may be compared to thresholdsrepresenting expected or prior average heartbeat force and/or rhythm forthe patient to determine any deviation from a norm. Similarly, otherpatterns indicative of arrhythmia or normal cardiac force/rhythm may bestored as templates and compared to the signal to detect the presence ofan arrhythmia or the absence of normal cardiac functioning.

If an arrhythmia is detected, then the device may send a signal to thepatient, care provider or physician, or record the event for laterobservation. The signal to the patient may be in the form of an audiblealarm. The signal to the care provider or physician may be in the formof an automated text messaging system using known telephonic circuitryand a subscription to a cellular provider. Immediate action andtreatment is therefore enabled which is particularly useful in view ofthe known co-morbidity involving cardiac conditions and respiratorydisorders such as SDB.

The determination of cardiac timing is possible by monitoring theaverage time between cardiogenic oscillations such as 50 and 52. Fromthis timing, heart rate parameters can be deduced such as average rate,variability and arrhythmia. All information regarding cardiac conditionsmay be observed in real time by way of suitable display, transmitted orrecorded. Ventilatory support may be modified so as to assist cardiacfunction where, for example, CPAP therapy pressure is changed accordingto the cardiac cycle to assist right atria filling (pressure decrease),left ventricular ejection (pressure increase), and cardiac perfusion(pressure increase at early diastole), etc.

It has been observed that cardiac stroke volume affects the amplitude ofcardiogenic oscillations and that CPAP treatment affects stroke volume.Therefore, by monitoring cardiogenic oscillations in accordance with thepresent invention, it is possible to titrate CPAP treatment so as toinfluence and preferably to optimize cardiac stroke volume. This may beachieved without uninterrupted monitoring of heartbeats. Rather it maybe achieved with the monitoring of only 1-2 heartbeats per breath, i.e.,by monitoring only during a portion of the respiratory cycle, preferablyduring the middle to end expiration portion. For example, stroke volumemay be maximized by examining the amplitude of the cardiogenicoscillations and servo-controlling the pressure treatment accordingly.

It has been proposed that pulse-transit time (PTT) may serve as anon-invasive means of inferring respiratory effort and arousals. The PTTis the time in which a pulse wave propagates the length of an arterialtree and is measured by the time interval that starts when half of theventricular myocardium has been depolarized and ends when the blood issaturated with a predetermined percentage (depending on the age andcondition of the patient) of oxyhemoglobin (SpO₂). The former occurswhen an R-wave is sensed in the ECG QRS complex (the entire time ittakes for depolarization of the ventricles), and the latter occurs whena typical finger pulse oximeter senses photoplethysmographic (pulse)waveforms.

The disadvantage of the typical measurements of the PPT is that thepre-ejection period (PEP) is included in the measured delay. The presentinvention allows for the achievement of a more accurate measure ofpulse-transit time (i.e., a measure of pulse-transit time without thepre-ejection period component). By performing uninterrupted monitoringof cardiogenic oscillations concurrently with pulse oximetry, PTT may beestimated. An advantage of the present invention is that it usescardiogenic oscillations for measuring cardiac timing. The cardiogenicoscillations relate to the heart's mechanical systolic events ratherthan the electrical systolic events, so the PEP is not included.

Changes in the heart's PEP can also be assessed by the concurrentmonitoring of cardiogenic oscillations against the ECG trace 42, andfollowing the lag in time between electrical and mechanical systolicevents. The changes in the PEP reflect the ability of the left ventricleto eject (perform mechanical systole events) and are another indicationof cardiac health, and blood pressure, as well as peripheral vascularresistance and other cardio-circulatory conditions of interest inpatient management.

In summary, the apparatus may be configured or programmed to do thefollowing while the patient is wearing a mask: measure airflow; identifyand isolate the cardiogenic signal from the airflow; identify centralapneas; calculate heart rate from the cardiogenic signal; determineabnormalities in heart rate (e.g., arrhythmias); generate notificationsif an abnormality is determined, where the notifications include analarm or other means of contacting selected individuals; monitor cardiactiming and assist in cardiac function; more accurately determinerespiratory effort; and monitor PTT and PEP.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not as restrictive. The scope of the invention is, therefore,indicated by the appended claims and their combination in whole or inpart rather than by the foregoing description. All changes that comewithin the meaning and range of equivalency of the claims are to beembraced within their scope.

1-24. (canceled)
 25. A method of a processor for determining a patient'scardiac oscillations and providing a pressure treatment with a pressureapparatus for treating breathing, comprising: sensing with a sensorcardiogenic pressure or flow oscillations of a patient; and with theprocessor, applying cardiogenic oscillation information for managingtriggering of the pressure apparatus.
 26. The method of claim 25 furthercomprising adjusting pressure delivered by the pressure apparatus. 27.The method of claim 26 wherein the applying comprises removal ofcardiogenic oscillations from a flow signal.
 28. The method of claim 27wherein the removal comprises filtering of the flow signal at anend-expiration portion of a breathing cycle.
 29. The method of claim 27wherein the applying further comprises determining when to cycle fromexpiration to inspiration with the flow signal.
 30. The method of claim25 wherein the applying further comprises changing the treatmentpressure to cycle from expiration to inspiration.
 31. The method ofclaim 30 wherein the pressure apparatus for treating breathing is asleep disordered breathing apparatus.
 32. Apparatus for determining apatient's cardiac oscillations and providing pressure for treatingbreathing, comprising: at least one sensor to sense cardiogenic pressureor flow oscillations of the patient; and a controller, the controllercoupled with the sensor and a pressure delivery device, the controllerincluding a processor configured to apply cardiogenic oscillationinformation from the sensor for managing triggering of the pressuredelivery device.
 33. The apparatus of claim 32 wherein the controller isconfigured to adjust pressure delivered by the delivery device.
 34. Theapparatus of claim 33 wherein the processor is configured to apply thecardiogenic oscillation information by removing cardiogenic oscillationsfrom a flow signal.
 35. The apparatus of claim 34 wherein the removingcomprises filtering of the flow signal at an end-expiration portion of abreathing cycle.
 36. The apparatus of claim 35 wherein the processor isconfigured to manage triggering by determining when to cycle fromexpiration to inspiration with the flow signal.
 37. The apparatus ofclaim 36 wherein the processor is further configured to managetriggering by changing treatment pressure to cycle from expiration toinspiration.
 38. The apparatus of claim 37 wherein the pressure deliverydevice is a sleep disordered breathing apparatus.
 39. A method of aprocessor for determining a patient's cardiac condition with a pressureapparatus for treating breathing, comprising: sensing, with a sensor,cardiogenic pressure or flow oscillations of a patient; and determining,with the processor, the patient's cardiac condition with the sensedcardiogenic oscillations and adjusting a stroke volume of the patient.40. The method of claim 39 wherein the adjusting comprises titratingpositive airway pressure treatment in accordance with monitoringcardiogenic oscillations.
 41. The method of claim 39 wherein thedetermining and the adjusting the patient's stroke volume comprisesexamining amplitude of the cardiogenic oscillations and in accordancetherewith adjusting a treatment pressure of the pressure apparatus. 42.The method of claim 41 wherein the adjusting comprises servo-controllingpressure of the pressure apparatus in accordance with the amplitude. 43.The method of claim 40 wherein the monitoring comprises interruptedmonitoring of heartbeats during a portion of a respiratory cycle. 44.The method of claim 43 wherein the portion comprises a middle to endexpiration portion.
 45. The method of claim 44 wherein the pressureapparatus for treating breathing comprises a sleep disordered breathingapparatus.
 46. An apparatus for determining a patient's cardiaccondition and providing a pressure for treating breathing, comprising:at least one sensor to sense cardiogenic pressure or flow oscillationsof a patient; and a controller, the controller coupled with the sensorand a pressure delivery device, the controller including a processorconfigured to determine cardiac condition with the sensed cardiogenicoscillations and to adjust a stroke volume of the patient.
 47. Theapparatus of claim 46 wherein the adjustment of the stroke volumecomprises titrating positive airway pressure treatment in accordancewith monitoring cardiogenic oscillations.
 48. The apparatus of claim 46wherein the cardiac condition determination and the adjustment of thestroke volume comprises examining amplitude of the cardiogenicoscillations and in accordance therewith adjusting a treatment pressureof the pressure delivery device.
 49. The apparatus of claim 48 whereinthe adjustment of the stroke volume comprises servo-controlling pressureof the pressure delivery device in accordance with the amplitude. 50.The apparatus of claim 47 wherein the monitoring comprises interruptedmonitoring of heartbeats during a portion of a respiratory cycle. 51.The apparatus of claim 50 wherein the portion comprises a middle to endexpiration portion.
 52. The apparatus of claim 51 wherein the pressuredelivery device comprises sleep disordered breathing apparatus.